Prior art positive resist images, such as those useful in the fabrication of integrated circuits, printing plates and the like, are generally prepared by coating a film or layer of an appropriate material such as a polymeric material onto a substrate, and then exposing portions of the film or layer to radiation such as electron beam, ultraviolet light and x-ray radiation in a predetermined pattern of the desired geometry with sufficient exposure to degrade the polymeric material in the exposed areas. Next, the electron beam degraded polymeric material is removed from the exposed area with a solvent which has a marked differential solubility for the exposed degraded products and for the unexposed polymeric material.
The energy dosage and exposure time in such processes need to be sufficient to provide a large enough difference between the molecular weight of the exposed and unexposed polymer to make it possible to remove the exposed degraded material without also removing a large proportion of the unexposed areas by dissolution in the selected solvent.
It is desirable and important in the manufacturing of devices such as integrated circuits by electron beam lithography or by other means of radiation, that the energy dosage and exposure time required for high resolution be as low as possible to provide a process which is both practical and economical to carry out.
Accordingly, it is an object of the present invention to provide a process whereby it is possible to employ relatively low energy dosages and/or low exposure times. Another object of the present invention is to provide a process which does not require a marked differential solubility for the exposed and for the unexposed polymeric materials.
Another object of the present invention is to provide a process for forming a positive resist image by exposure to radiation such as electron beam radiation, x-ray, and ultraviolet light which employs a polymeric material of improved resist sensitivity and resolution.
Another object of the present invention is to provide a process for the formation of high resolution polymeric positive resists utilizing a radiation activated polymer of certain polymeric materials containing polymerized alkyl methacrylate units, which polymer exhibits excellent film-forming characteristics, resistance to various etch solutions, and ready removal of unexposed portions with simple solvents.
The use of certain alkyl methacrylate polymers as radiation degradable and particularly electron beam degradable polymers for the formation of resist masks which are useful in the fabrication of integrated circuits, printing plates, and the like has been proposed heretofore. For instance, U.S. Pat. No. 3,538,137 granted on Oct. 20, 1970 to Haller et al teaches among other things the use of methacrylate polymers containing a quaternary carbon in the polymer backbone such as polymethyl methacrylate, and copolymers of methyl methacrylate with 2-hydroxy ethyl methacrylate, for such purpose. In addition, U.S. Pat. No. 3,779,806, granted on Dec. 19, 1973 to Gipstein et al discloses the use of certain polymers of t-butyl methacrylate for such purpose.
Related discussions are contained in the articles "Polymethyl Methacrylate as an Electron Sensitive Resist" by R. A. Harris, J. Electrochemical Society, Vol. 120, No. 2, pp. 270-274, Feb. 1973, and "A Modified Methacrylate Positive Electron Resist" by E. D. Roberts, Applied Polymer Symposium, No. 23, pp. 87-98 (1974). For a discussion of employing polymethyl methacrylate in x-ray lithography, see "X-Ray Lithography - A New High Resolution Replication Process" by D. L. Spears et al, Solid State Technology, July 1972. pp. 21-26.
Also, certain modified alkyl methacrylate polymeric materials have been suggested by Gipstein et al for increasing the sensitivity to electron-beam radiation, IBM Technical Disclosure Bulletin, Vol. 16, No. 9, February 1974 - Sensitive Positive Electron Beamed Resists, and U.S. Pat. application Ser. No. 545,063 filed Jan. 29, 1975.
The use of polymethyl methacrylates suggested heretofore has apparently been limited to techniques in semiconductor processing which employs temperatures not exceeding about 130.degree. C (see M. Hatzakis, Journal Electrochemical Society, 116, 1033, 1969). Accordingly, it is an object of the present invention to provide a process wherein the polymeric materials employed have increased thermostability as compared to polymethyl methacrylate homopolymers. It is an object of the present invention to be able to provide semiconductor processing such as sputter etching, ion-beam etching, ion-beam doping, or lift-off metallurgy techniques wherein the polymeric material can be subjected to relatively high temperatures, i.e., above about 135.degree. C.